The present invention relates to a system and a method for starting the engines of a twin-engine aircraft.
Between two flights of an aircraft, the time that elapses between disembarkation and boarding is between thirty minutes and one hour. During this time, the airplane engines which are stopped remain hot and do not have time to cool completely before the next take-off and so a residual thermal gradient at the rotors of the engines causes the rotor shaft to expand (this being the phenomenon referred to as “bowed rotor”). At the restart, if the engine has not had time to cool sufficiently, some of the tips of the rotor blades may rub against the casing.
It is known practice, in order to prevent this phenomenon, to proceed, when starting an engine, with spinning up of a rotor of the high-pressure stage of the engine (rotor N2) progressively with a holding stage during which the rotational speed of said rotor is limited, for example to approximately 10% of a nominal rotational speed (this limit is dependent on the type of engine).
The purpose of the holding stage is to allow the temperature of the rotor to become uniform, and this stage may last up to 5 minutes. Therefore, when the two engines are started in succession as the regulations demand, it is necessary to wait for a minimum of 10 minutes after boarding the passengers before the two engines are fully operational for take-off.